1. Field of the Invention
The present invention relates to a novel method for measurement of dynamic water break resistance capable of predicting a degree of paper-breakage at the time of offset printing and to an apparatus for carrying out this novel method for measurement of dynamic water break resistance.
2. Description of the Related Art
Usually, a printing paper is required to have sizing properties to a some extent. Though this requirement to sizing properties is somewhat different depending on the nature required by a printing method employed, sizing has hitherto been to prevent a bleeding phenomenon of an ink when writing with a pen on paper. Accordingly, as a method of measurement for such sizing, one by which a degree of the bleeding phenomenon can be evaluated was sufficient, and it could be sufficiently achieved only by measuring the spreading of an ink on the surface of a paper layer or the penetration of the ink in the thickness direction.
As a method for measurement of the spreading of the ink on the paper surface, for example, there is known a carpentry sizing test method for electrically measuring the surface resistance of paper.
However, in rotary printing for subjecting a paper to continuous roll printing at a high speed and particularly, in a high-speed offset rotary printing in which a dampening water is used, the resistance to water absorption to a paper is important. This is because decrease in of the tensile strength of paper by water absorption results in paper-cutting. That is, in a method for measurement to represent a degree of bleeding phenomenon of an ink as in, for example, the conventional carpentry sizing test, it was difficult to precisely evaluate the water break resistance in the high-speed offset rotary printing.
A newspaper rotary press is a machine for undergoing high-speed printing using a roll paper, cutting and folding. Specifically, it is constituted from respective parts of (1) a paper-feeding part, (2) a printing part, (3) a color printing part, (4) a folding part, (5) a rail frame part, and (6) a driving part. In this newspaper rotary press, there is a sheet-run between the paper-feeding part and the printing part, between the printing part and the color printing part, and between the color printing part and the folding part, respectively. In this sheet-run, the tension of paper during running must be controlled. This is because if the tension is low, overlap, twist, or the like may likely occur, while if it is too high, wrinkling or paper-cutting may likely occur. In the case of newspaper rotary offset printing with an A-winding width, though in monochromatic printing, a tension of 40 kgf is usually applied, in color printing, a tension of from 70 to 80 kgf is applied in order to avoid the overlap. On the other hand, in the newspaper rotary offset printing, in order to control a loss in finish printing caused by blackening as low as possible, an excess of a dampening water is used at the time of start of the printing or of the replacement of a printing plate. Further, the dampening water retains in a space in a blanket joint, whereby the dampening water may attach onto a paper surface in a line to the width direction.
In this connection, it is considered that if an excess of water attaches onto a paper surface and penetrates into an interior of the paper layer, the tensile strength of the printing paper is lowered, thereby likely causing paper-cutting. For this reason, the sizing of paper, i.e., the resistance of water absorption, is required. In particular, in the case of color printing, the dampening water is brought into contact with the paper surface four times at one printing step. Accordingly, it is feared that even if a small amount of water attaches onto the paper surface, in case that the resistance to water absorption of paper is low, the water penetrates into an interior of the paper layer, whereby the tensile strength is markedly lowered. On the other hand, it is considered that in case where the resistance of water absorption is high, and the amount of water which penetrates into an interior of the paper layer is small, even if an excess of the dampening water attaches to the paper surface, the tensile strength is not lowered so much.
However, according to the conventional methods for measurement of sizing, in a sense of the counter measure for the paper-cutting, it was impossible to precisely grasp what extent of sizing (resistance to water absorption) is necessary for a paper to have high-speed offset printability. In other words, it was impossible to numerically express what extent of sizing (resistance to water absorption) is necessary for a printing paper which is desired for high-speed offset printing.
As a method for measuring both the sizing and strength of paper, there is a wet tensile strength test for measuring the tensile strength after immersing a paper in a distilled water as indicated in JIS P8135. This wet tensile strength test is one in which the whole of a paper specimen is immersed in a distilled water, whereby the tensile strength is measured in a completely wet state. However, this test is to be carried out under severe test conditions different from the water absorption state at the time of the actual offset rotary printing. Accordingly, it was impossible to apply this wet tensile strength test to products having a low sizing as in newspaper printing paper. Thus, in particular, it was impossible to quantitatively measure a degree at which the paper-cutting as actually generated by the attachment of an excess of the dampening water in the offset rotary printing occurs.
As described above, it is considered that in order to avoid a paper-cutting problem in the continuous offset rotary printing using a roll paper, previously grasping the physical properties of paper regarding the paper-breakage and in particular, controlling the resistance to water absorption of the paper is considered possible to avoid such trouble.